An object of the present invention is to provide a nanotube-nanohorn complex having an aspect ratio higher than that of a conventional one, also having high dispersibility, and being capable of growing carbon nanotubes with controlled diameter. A nanotube-nanohorn complex according to the present invention comprises carbon nanohorn and catalyst fine particles supported within the carbon nanohorn. The carbon nanohorn comprise an aperture formed therein. Each of the catalyst fine particles is fitted and fixed in the aperture in a state in which part of the catalyst fine particle is exposed to the exterior of the carbon nanohorn. Carbon nanotubes are grown from the catalyst fine particles.